1. Field of the Invention
The present invention relates to a polishing method and apparatus, and more particularly to such a method and apparatus for polishing a workpiece such as a semiconductor wafer. Further particularly, the present invention relates to such a method and apparatus wherein a workpiece to be polished and washed, particularly a dry workpiece, is loaded into the apparatus, is polished and then washed and dried therein, and wherein the resultant clean and dry polished workpiece is transferred from the apparatus. When a dry workpiece to be polished is loaded into the apparatus and a clean and dry polished workpiece is transferred from the apparatus, the method is referred to hereinafter as a "dry-in, dry-out" method. Still further particularly, the present invention relates to such a "dry-in, dry-out" method and apparatus including a plurality of operating units disposed in an array or cluster around at least one center robot having at least one robot arm, and having a transfer structure including separate and discrete transfer mechanisms including at least one first transfer mechanism for transferring a dry workpiece into the apparatus and for transferring the clean and dry polished workpiece from the apparatus, and at least one second transfer mechanism for transferring the workpiece between polishing and washing units of the apparatus.
2. Description of Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnections is photolithography. Although a photolithographic process can form interconnections that are at most 0.5 .mu.m wide, such process requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat to enable use of photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus.
Conventionally, such a polishing apparatus has a single function of polishing a semiconductor wafer. Therefore, in the case of washing a semiconductor wafer after polishing, the semiconductor wafer must be transferred or transported from the polishing apparatus to a washing apparatus. Further, in the case of polishing a semiconductor wafer again under different conditions after a first polishing operation, the semiconductor wafer must be transferred or transported from one polishing apparatus to another polishing apparatus. In such cases, the semiconductor wafers are manually transferred or transported by a movable container in which they are immersed in water to keep them from drying during transportation. However, since various apparatuses including a polishing apparatus and a washing apparatus are independently installed and the semiconductor wafers are transferred or transported by the movable container containing water therein, it is difficult to install the polishing apparatus, the washing apparatus and the like in a clean room of a semiconductor manufacturing plant and to automate completely various processes including a polishing process and a washing process.
In order to solve the above problems, there has been proposed an apparatus which has a polishing unit and a washing unit provided in a common housing. Further, if necessary, a plurality of polishing units can be provided in a common housing. In a polishing apparatus which has a polishing unit and a washing unit, or a plurality of polishing units in a common housing, it is conceivable to construct a cluster type of polishing apparatus which integrates a plurality of units including a polishing unit and a washing unit, as employed in a semiconductor manufacturing process such as etching or chemical vapor deposition (CVD).
However, in the case of constructing a cluster type of polishing apparatus which integrates a plurality of units and incorporates a universal transfer robot at a central position of the units, it is necessary to handle both a dirty and wet semiconductor wafer soiled with abrasive slurry or particles generated by the polishing operation and a clean and dry semiconductor wafer which is placed on a loading unit or an unloading unit. Therefore, a conventional robot incorporated in a cluster type of a semiconductor manufacturing processing apparatus cannot be used in a cluster type of polishing apparatus because such robot is not capable of handling separately both a clean semiconductor wafer and a dirty semiconductor wafer. If such conventional robot is incorporated into the polishing apparatus, a washing process and a drying process of the robot or a robot arm additionally are required, thus lowering throughput efficiency of the apparatus. Further, when such robot or the robot arm is left for a long time as it is, abrasive material or particles generated by the polishing operation adhere to the robot or the robot arm, resulting in contamination of subsequent semiconductor wafers or respective units of the polishing apparatus.